Electrical loading apparatus



June 2e, 1962 w. s. PRITCHETT 3,04 6

- LOADING APPARATUS v Sheet 2 Filed July 11, 1958 4- 1 k l; 25 \unmuui 1 grip?! INVENTOR. WILSON S. PR/TCHETT BY I WWIM A T TORNE VS June 26, 1962,

ELECTRICAL LOADING APPARATUS V Filed July 11, 1958 5 Sheets-Sheet s v INVENTOR. W/LSO/V S. PR/TCHETT 58 BY Z 7 M WwZ A TTO/PNEVS w. s. PRITCHETT 3,041,464

3,041,464 Patented June 26, 1962 3,041,464 ELECTRICAL LOADING APPARATUS Wilson S. Pritchett, Richmond, Calif., assignor to Knopp, Inc., (lalcland, Calif, a corporation of California Filed July 11, 1958, Ser. No. 747,863 6 Claims. (Cl. 30717) This invention relates to electrical loading apparatus and more particularly to apparatus providing a variable supply of current or voltage over a wide range.

In performing certain testing functions, for example, testing current transformers, a current supply is required that is variable over a wide range. For many other current loading applications it is desired to provide a current output varying from zero to many thousands of amperes.

Heretofore the use of auxiliary loading transformers or tapped loading transformers coupled with limited range variable sources have been proposed for achieving these purposes. Several difliculties are attendant upon using such prior art apparatus, however, because of the high voltages carried by the unused windings and other inherent limitations in the range and controllability of such devices. Prior known high capacity variable current supplies are also unduly complicated and very expensive to build and maintain.

It is therefore a main object of this invention to provide wide range electrical loading apparatus which is relatively simple and inexpensive to build, control, and maintain.

Another object of this invention is the provision of current loading apparatus having ranges to many thousands of amperes without overloading portions of the apparatus on the lower ranges.

It is still another object of this invention to provide a high capacity variable electrical supplying apparatus having smooth control throughout its wide range.

A further object of this invention is the provision of high capacity variable current loading apparatus having safety control means for preventing large current surges.

A still further object of this invention is the provision of wide range variable electrical loading apparatus to which incremental supply units may be relatively easily added to increase the output range of the apparatus.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a schematic circuit diagram of the preferred form of the apparatus of this invention;

FIG. 2 is a schematic diagram of a control circuit for use with the apparatus of 'FIG. 1;

FIG. 3 is a top plan view of a preferred structure of a high current loading apparatus of FIG. 1;

FIG. 4 is an enlarged transverse sectional view as seen from line 44 of FIG. 3;

FIG. 5 is a schematic circuit diagram of a variable supply device for use with the apparatus of FIG. 1;

FIG. 6 is a modified form of the structure of FIG. 3 I

for use in relay testing and the like; and

FIG. 7 is an enlarged sectional View as seen from line 7-7 of FIG. 6.

In detail, the apparatus of this invention comprises a plurality of electrical supply devices (FIG. 1), generally designated 1, 2, 3, 4, adapted to be connected in series across a load, generally designated 5. In the example illustrated, load 5 is a current transformer under test to which it is desired to apply the output of devices 1, 2, 3 and 4, although it will be understood that any other suitable load may be connected between the terminals 6 of the bus bar 7 connecting devices 1, 2, 3, 4 in series.

The electrical supply devices 1, 2, 3, 4 illustrated in FIG. 1 are transformers having primaries 11, 12, 13, 14 respectively. These primaries are electro-magnetically linked through cores 15 to secondaries which, in the example shown, comprise bus bar 7. In effect, bus bar 7 comprises a single turn secondary common to and linking the cores 15 which also are linked respectively by primaries 11, 12, 13, 14.

A preferred, detailed construction of the transformers serving as supply devices 1, 2, 3, 4 will be later described, and it will be understood that each may have its own separate secondary, as desired, connected in the series arrangement shown. The form illustrated, in which bus bar 7 serves as both the secondary to the transformers as well as the means connecting said secondaries for delivering the output to the load 5, is preferable because of the high current which bus bar 7 is intended to carry.

The input to the primary 1-1 of device 1 is intended to be varied as by a variable auto-transformer device 16 (FIG. 1). Said variable device may be of the conventional type known under the trade name Variac which is connected across primary 11 for providing a variable input thereto from zero or some negligible value to the capacity of device 1. Hence, primary 11 along with autotransformer 16 will hereinafter be known as the variable electrical supply device designated by numeral '1.

Devices 2, 3, 4, on the other hand, are fixed output electrical devices in that they provide either no output or their full capacity output to the circuit. Each of the devices 1, 2, 3, 4 is connected across main power source 17 through main lines 18 having on-oif switch 19 therein. Source 17 provides excitation for primaries 11, 12, 1-3, 14 thereby energizing the supply transformers 1, 2, 3, 4.

In the circuits to primaries 12, 13, 14 of devices 2, 3, 4 double throw switches 22, 23, 24 are respectively provided. In one position each of these switches completes a circuit from main power line 18 to its associated primary. In the opposed position each of these switches short circuits its respective primary. Switches 22, 23, 24 are individually operable and thereby provide means for individually completing the power circuits to primaries 1'2, 13, 1 4 for energizing the same and means for individually short circuiting said primaries for de-energizing the same. In this manner each of the devices 2, 3, 4 either supplies its full capacity of output to the total applied to bus bar 7 or it supplies no output when its primary is short circuited, although current may flow in its primary while short circuited.

In the current transformer testing application illustrated in FIG. 1 a standard current transformer 10 may be included in the circuit with devices 1, 2, 3, 4 and the transformer under test 5 for the conventional purpose of measuring the current flowing through bus bar 7 into the transformer load 5. Connections are shown to the terminals of a conventional transformer test set 8 for measuring the ratio and phase errors of the transformer 5 under test by the known dilferential or comparative method.

The design of supply transformers 1, 2, 3, 4 may be chosen to suit the particular requirements and capacity desired for the unit. In the preferred design illustrated in FIGS. 3 and 4 the primaries 11, 12, 13, 14 of said transformers are wound in the form of four identical coils, connected in either parallel, series-parallel or series, with each coil wound on one leg of a rectangular core 15 (FIG. 4) having a central opening 20 therethrough. The core '15 may be of the type formed from strips of a suitable magnetizable material laminated in the open rectangular form shown and secured together with rivets 21 or the like. The coils separately wound on each leg of the core 15 function together as the primary 12 (FIG. 4) as a result of being properly connected together. It will be noted that the electrical connections to the ap 3 paratus of FIGS. 3 and 4 are not shown thereon but are intended to be the same as those shown in FIG. 1.

The secondaries of the transformers 1, 2, 3, 4, comprising bus bar 7 may be fabricated from a plurality of spaced, stacked bars 25 (FIG. 4), of copper or other good electrical conducts, passing through the central opening 20 in each of the supply transformers. Said transformers 1, 2, 3, 4, as well as the standard transformer 10, of like construction, may be received in an aligned group on bars 25 with the opposite end of said bars projecting oppositely outwardly from the group. A similar set of bars 26 (FIG. 3) may have their ends interposed in the spaces between the ends of bars 25 and be connected thereto by suitable means, such as bolts 27, for projecting transversely of bars 25. The loop circuit of bus bar 7 is completed through the load by a third, similar set of bars 28, similarly connected by bolts 29 to the outer ends of bars 26.

Bars 28 project oppositely inwardly toward each other to provide terminals 6 at their inner adjacent ends for connection to the transformer under test or other load 5. Preferably, bars 28 are slotted, as at 30, providing movement of terminals 6 toward and away from each other for accommodating the various types of terminals which may be carried by the transformer under test. The ends of bars 28 which comprise terminals 6 will easily accommodate either multiple leaf or single leaf fish tail type terminals on the transformer under test, or, terminals 6 may be connected together for receiving a conventional through type transformer connected as a load 5.

In operation, with the load 5 connected as shown in FIG. 1 and with switches 22, 23, 24 all in the de-energized positions short circuiting primaries 12, 13, 14, current is supplied through bus bar 7 to the load by variable supply device 1 alone. On this lowest range variable device 1 provides an electrical supply from zero to a maximum which may be some fraction of the maximum current desired to be applied to the load 5. Greater current is supplied to load 5 by first returning the variable device to zero or negligible output and then by energizing one of the fixed supply devices 2, 3, 4 by throwing its corresponding switch 22, 23 or 24 from the de-energized position to the energized position completing the circuit from main line 18 to its associated primary 12, 13, or 14. Each of the fixed devices 2, 3, 4 is designed so as to have an output capacity of slightly less than the output capacity of variable device 1 and therefore throwing switch 22, for example, to the on or energized position causes fixed device 2 to supply its full capacity output to bus bar 7 and hence to the load 5.

During this succeeding range the current supplied to load 5 may then be adjusted by variable device 1 from the output capacity of fixed device 2 (which is a little lower than the full output capacity of variable device 1) to a value almost twice the output capacity of variable device 1. In other words, device 1 provides a supply of controllable output from zero to approximately onefourth, for example, of the maximum output that may be desired to be applied to the transformer 5' under test. Fixed device 2 adds its increment of approximately another one-fourth of the desired maximum, which then extends the range of comtrollability of the output supply by device 1 from one-quarter to one-half of the desired maximum. In a similar manner fixed devices 3 and 4 are designed to supply approximately one-quarter of the desired maximum output when energized in the manner described, thereby extending the range of adjustability of device 1 successively from one-half to three-quarters and from three-quarters to full maximum output to the load 5.

In effect, this invention provides a plurality of individual electrical supply devices or transformers connected in series with a load and each having an output capacity of a fraction of the maximum output desired to be applied to the load and with the sum of said capacities being substantially equal to said maximum output. One of the supply devices is provided with means for varying its output from zero to its capacity, whereas the other of such devices may be individually short circuited or de-energized and energized to add their output capacities in increments to cause the current to flow through the load. It will be obvious that additional fixed supply devices, such as devices 2, 3 and 4, may be added to the circuit to provide whatever range is desired.

For example, in the device illustrated in FIG. 1 variable device 1 may have a 29 kva. capacity and be provided with one hundred turns in its primary 1 1. Devices 2, 3 and 4 may be 24 kva. transformers having turns in their respective primaries. Given a suitable main power source 17 and assuming that bus bar 7 acts as a single turn secondary for each of the devices 1, 2, 3 and 4 the assembled apparatus will deliver a closed circuit current to the load 5 variable from zero to approximately 12,000 amperes.

With the primaries of devices 2, 3, 4 all short circuited variable device 1 will deliver a current to load 5 variable from zero to approximately 4,000 amperes. With the primary 12 of device 2 energized the current delivered to load 5 may be varied between approximately 3,333 amperes and 7,350 amperes. The variable range is extended, by additionally energizing the primary 13 of device 3, from approximately 6,667 amperes to 10,700 amperes; and throwing switch 24 to energize primary 14 of device 4 increases the range from approximately 10,000 amperes to 14,000 amperes.

It will be noted that the auto-transformer or like variable control means 16 adjusts the current applied to the load over a fraction only of the total range of the assembled apparatus. For this reason, as the current applied to load 5 is increased by energizing a greater number of r the fixed supply devices, the range of adjustment of device 16 thereby becomes a smaller percentage of the total current flowing through the load. In this manner the current adjustment through variable device 16 becomes succeedingly smoother in the higher current output ranges. Since the steps in the ranges preferably overlap because of the difference in capacities of the variable supply device and the fixed supply devices, relatively smooth current adjustment up to very high values is provided. This smooth control is particularly desirable where the apparatus of this invention is used for loading trans formers under test and it is necessary to accurately set a specified value of current.

As a safety measure, where high output supply devices are used, it is highly desirable to return the Variac or variable supply device 16 to zero current output before switching on or energizing the successive fixed supply devices. It is clear that if variable device 1 were'operating at or near capacity, energizing any one of the fixed supply devices 2, 3, 4 would cause a high current surge at an advanced range which may create a temporary overload and possibly damage the apparatus.

Provision is made, therefore, for the interlocking control circuit of FIG. 2 to prevent such an occurrence. Said control circuit is provided with a power source 31, either auxiliary to or included in mainsource 17, across which are provided parallelcircuits including the switches 22, 23, 24. Said switches are shown in the de-energized or short circuited positions in which they are held by springs 35. Switches 22, 23, 24 are each adapted to be closed to the energized position against the urgency of spring 35 by an individual corresponding electromagnetic coil 36. Between switches 22, 23, 24 and their operating coils 36 are corresponding operating switches 32, 33, 34.

In parallel with each of the circuits including operating switches 32, 33, 34 and coils 36 isa second circuit including a switch 37. Switches 37 are ganged for operation together, as shown, and are normally in the open position interrupting their associated parallel circuits. Switches 37 are closed by a relay coil 38 connected to power source 31 by a circuit including a switch 39. The

dotted line 40 (FIGS. 1 and 2) indicates a mechanical linkage between switch 39 and the variable control device 16 such that switch 39 will be closed only when said variable device is in the zero position, that is, device 1 is delivering either negligible or no output to load 5.

With switch 39 in the open position, 'when variable de vice 1 is delivering any appreciable output to load 5, closing any of the switches 32, 33, 34 will have no effect because of the interruption of both the circuits to coil 36 by switches 37 and switches 22, 23, 24. When the Variac is in the zero position, however, switch 39 will be closed thereby energizing relay coil 38 to close switches 37. Closing a switch 32, for example, in this situation thereby completes the circuit through its associated coil 36 which will operate the corresponding switch 22 to a position energizing the primary 12 of the transformer 2. Adjusting the Variac away from the zero position will again open switch 39 and allow switches 37 to open thereby interrupting the circuits to the coil 36 operating switches 23 and 24. The coil 36 associated with switch 22 will, however, retain such switch in the on position energizing primary 12 because switch 22 itself completes the other parallel circuit from supply 31 through the corresponding coil 36. The control circuit of FIG. 2 thereby prevents the energization of any of the fixed supply devices 2, 3, 4 by their associated switches 22, 23, 24 except when the variable supply device 1 is in the zero position or delivering only negligible output.

The apparatus of this invention thereby provides a current output in smooth, overlapping, adjustable ranges up to very high values by means of relatively simple and inexpensive equipment. The range of such apparatus may be extended as desired and safety of operation is assured by interlocking control means such as described herein.

In modifying the apparatus of FIG. 1 for use in loading an electric furnace or the like, the variable means, generally designated 41, of FIG. 5 may replace variable device 1. Variable supply device 41 comprises a transformer primary 42 adapted to be electromagnetically linked by a core 43 to secondary bus bar 7 and having power leads 44 connectable to a power source, such as 17. A double throw switch 45, similar to switches 22, 23, 24, for connecting said primary 42 to said power source for energizing the same or for short circuiting and thereby deenergizing the same, in the opposed position.

Primary 45 is also provided with taps 46, 47, 48 which may be individually connected to a power lead 44 by switch 49. The output of transformer 41 may in this manner be adjusted by energizing a lesser or greater number of turns of primary 42 by switching to one of the taps 46, 47 or 48. This adjustment is in discrete steps rather than the indiscrete variability of device 16 of FIG. 1.

To avoid an overly high voltage on the unused windings of primary 42 it is preferable that the steps of adjustment be no greater than one-half the output capacity of transformer 41. In other words, tap 46 should be located no nearer to the untapped side of primary 42 than the center of said primary. The other transformers 2, 3 and 4 of the combination of FIG. 1 may likewise be provided with step adjustment devices to provide various combinations of adjustability. At least one of the supply devices should be adjustable to perform the unique results of this invention.

FIGS. 6 and 7 disclose structural details of the apparatus of this invention modified from that of FIGS. 3 and 4. In the former the loading transformers or supply devices 51, 52, 53, 54, 55 and 56 are each provided with ringtype cores 65 having suitably insulated primary coils 5-8 wound on one side thereof. Said transformers may be supported on an elongated base member 60 in aligned adjacent pairs with the legs of a U-shaped or hairpin type bus bar secondary 57 (FIG. 6) extending through the windows 64 of their cores 65 (FIG. 7). Said bus bar is 6 provided with terminals 66 (-FIG. 6) at its ends for connection to a relay to be tested or like load.

The connections to transformers 51 to 56 are substantially the same as those to transformers 1-4 of FIG. 1 and the former may each be provided with a convenient receptacle 59 for connection of a variable device, such as 16, to one of said transformers 51-56, and for connection of deenergizing switches, like 2224, to the others.

The convenience of the device of FIGS. 6 and 7 is its demountability and resulting portability. For example, a single 30 kva. unit for this purpose would weigh at least 300 lbs. Each of the units 5156 of the above description would only weigh about 65 lbs. and in the combination shown and described could provide the same 30 kva. This combination may therefore be easily disassembled and moved to a location close to the testing site without the use of heavy equipment.

The use of base member 60, cut to receive a portion of the ring cores (FIG. 7), aids in the assembly of the com bination of FIG. 6 as the transformers 51-56 may be laid in said base member and bus bar 57 slipped through the core windows as shown. Suitable insulating means for said bus bar should be provided.

A top member 61 (shown in FIG. 7 and removed from FIG. 6) of similar configuration to member 60 may be placed over said transformers and said members secured together, as by bolts through holes 63 ('FIG. 6), for fixing transformers 51--56 together as a unit. Insulation strips, at 62 (FIG. 7), will effectively insulate members 60, 61 from cores 65.

Although the invention has been described and illustrated in detail, such as not to be taken as restrictive thereof or otherwise limiting the spirit and scope of the appended claims.

I claim:

I. Wide range variable electrical loading apparatus, comprising: a plurality of individual transformers having their secondaries connected in series with a load, each of said transformers having an output capacity of a fraction of the maximum output desired to be applied to said load and the sum of said capacities being substantially equal to said maximum output, one of said transformers having variable control means for delivering a variable output, and means for individually short-circuiting the primaries of the other of said transformers, whereby each of said other transformers may be energized individually to add its output capacity to the output applied to said load.

2. Wide range variable electrical loading apparatus, comprising: a plurality of individual transformers having their secondaries connected in series with a load, each of said trans-formers having an output capacity of a fraction of the maximum output desired to be applied to said load and the sum of said capacities being substantially equal to I said maximum output, one of said transformers having variable control means for delivering a variable output, and means for individually short-circuiting the primaries of the other of said transformers whereby each of said other transformers, may be energized individually to add its output capacity to the output applied to said load, the secondaries of said transformers comprising an elongated bus bar connectable at its opposite ends to said load, and the primaries of said transformers each being wound on a core having an opening for receiving said bus bar therethrough.

3. Electrical loading apparatus comprising:

(a) a plurality of electrical output supply devices each having an electrical energy input element, an electrical energy output element, and a separate magnetic circuit linking said elements,

(12) means for connecting said output elements serially with a load,

(0) adjusting means for adjusting the electrical energy supplied to one of said input elements,

(d) energizing means for individually connect-ing and disconnecting each of said input elements to a fixed source of electrical energy, and

(e) means for protecting the magnetic circuit of a disconnected input element from saturation.

4. The combination of claim 3 including:

(f) the output capacities of said devices being approximately equal.

5. The combination of claim 3 including:

(7) control means interconnected between said adjusting means and said energizing means disabling the latter when the electrical energy supplied to said one input element is other than negligible.

6. Variable electrical loading apparatus comprising:

(a) a plurality of transformers, each having a primary,

a secondary and a separate magnetic circuit,

(b) means for connecting said secondary serially with a load,

(c) adjusting means for adjusting the electrical energy supplied to the primary of one of said transformers,

(d) connecting means for individually connecting each of said primaries to a fixed source of electrical energy, and

(e) means for short-circuiting said primaries.

References Cited in the file of this patent UNITED STATES PATENTS 520,970 Scott June 5, 1894 529,152 Zickerrnan Nov. 13, 1894 740,174 Peck Sept. 29, 1903 765,236 Gaiife July 19, 1904 1,007,480 North et al Oct. 31, 1911 1,007,482 Peck Oct. 31, 1911 1,831,886 Ross Nov. 17, 1931 

